1. Field of the Invention
This invention relates to a document scanning apparatus such as, for example, one to be used in a copying machine, facsimile machine, image scanner or the like.
2. Discussion of Background
In a copying machine of the above-noted type, there is typically provided a lamp, a first optical scanner system including a first mirror and a second optical scanner system including a second mirror for illuminating an original during a scanning time. The first and second optical scanner systems are moved in the same direction at a 2:1 speed, so that the length of the optical path from the original to a photoconductive member is kept constant at all times, whereby an accurate image of the original is formed on the photoconductive member. In a copying machine capable of changing the magnification of a copying image, a lens moving mechanism and a mirror moving mechanism are provided in order optically downstream of the second optical scanner system to move a lens and mirrors according to a selected magnification ratio.
In such a document scanning apparatus, the mirrors of the first and second optical scanner systems should be mounted in perpendicular relationship with the lens. This perpendicular relationship of the mirrors with respect to the lens is produced by using a guide rod and arranging a bearing coupling the guide rod at a right angle relative to the mirrors of the first and second optical scanner systems. During assembling, an adjustment of the focus and the magnification ratio is done such that a standard chart is placed at a location where an image of the original is to be formed. Then an image of the standard chart is projected back to the location where the original is placed, and the length of optical path is adjusted by changing the position of the lens and/or the position at which a driving wire is clamped to the first optical scanner system.
However, even if the first and second optical scanner systems and the lens are respectively located at the best possible focusing positioss in the document scanning apparatus by means of the above described technique, when this document scanning apparatus is used in the field, misadjustment or accidents such as produced, for example, by breaking orstretching of a driving wire may happen. In these cases, it is necessary to replace and/or reclamp the driving wire and then to readjust the focus.
But in a prior art document scanning apparatus, the reclamping and focus readjusting unavoidably relys on the sixth sense of the servicemen, who must determine the correct clamping position by a trial and error process including making a copy of an image, reviewing the copied image, making an adjustment and then repeating this cycle.
On the other hand, it is not practical to uses the alignment and focus technique employed in the origincl factory assembly of the scanner apparatus in the field, because to do so would require a significant amount of extra equipment to be at the disposal of the servicemen, not to mention the problem of transporting the extra equipment to the user's site in the field, even if it were assumed that the extra equipment were available.